This invention relates generally to the recovery of energy from a slurry source which has substantial potential energy due to the elevation of the source above a working point and, more particularly, is concerned with the conversion of such potential energy into electrical energy.
In certain mining operations a metal-bearing ore is mined, crushed and milled at a mine site. Thereafter processed water is added to the milled product to produce a slurry at a predetermined specific gravity.
In a mountainous region such as Chile mining often takes place at a high altitude. The slurry which is produced at the mine site is then fed under gravity action via a pipeline to a process plant, at a relatively low altitude, at which minerals are extracted from the slurry.
In one mining operation known to the applicant the pipeline has a diameter of about 600 mm and has a length of the order of 50 kilometers. The difference between the heights of the mining site and the process plant is approximately 2500 meters. The substantial static hydraulic head coupled with the specific gravity of the slurry mean that the pressure at a discharge end of the pipeline can be as high as 400 bar. A pressure of this order is technically difficult to handle and constitutes a considerable potential danger. To obviate difficulties of this nature the slurry is passed through a series of pressure reducing or choke stations, at suitable intervals along its length, and at each station energy in the slurry is dissipated.
At the process plant the slurry is subjected to a solid/liquid separation step. The recovered solids undergo further processing for mineral recovery and the liquid, which essentially is clear process water, is pumped to the elevated mine site for reuse. The consumption of electrical energy in pumping the water to a height of about 2500 meters is considerable.
An object of the present invention is to provide a system which makes use of the potential energy in a slurry pipeline to generate electrical energy, which in part offsets the amount of energy required to pump the process water back up to the mine.